The environmental impact of residues resulting from industrial activity has been a concern to the society. Specifically, concerning the cork industry, relevant on the Mediterranean and specifically in the Portuguese economies, the last being world leader in cork production, accounting for circa 80% of world production, a relevant production of industrial residues is observed. As an example, cork stoppers production, the more relevant of the cork industrial sector, only uses about 25% of the original raw material. These residues or wastes are classified essentially based on granulometry, density and moisture, parameters that depend on the source of the materials along the manufacturing of commercial cork. An important amount of these wastes are granules used on a variety applications, mainly composite materials, namely cork/rubber, among others, such as component of low density sandwich materials used for aerospace applications, thermoplastics/cork agglomerates, agglomerated wine closures, cork composites, etc. On the other hand, the transforming industry generates a residue considered problematic, obtained across multiple production phases, including granulation, that is, value-added operation of residues to manufacture alternative cork based wine closures, which is an important fraction of the total amount of wastes with no commercial value, this is the so called “cork dust” (Cork Supply, 2010; S. P. Silva, M. A. Sabino, E. M. Fernandas, V. M. Correlo, L. F. Boesel, R. L. Reis, International Materials Reviews, 50 (6), p. 345, 2005).
The “cork dust” as the name suggests, includes small size particles, usually a size too small (<0.5 mm) for any possible reuse, due to its high surface. According to the Portuguese standard (ISO 633:2011) it has dimensions below 0.25 mm (L. Gil, Biomass & Bioenergy 13 (1-2), p. 59, 1997). Even when used for agglomerates, inclusion of the dust is only possible under small amounts, therefore not incorporating significant volumes compared to the production. Moreover, not only cork dust but also other residues of this industry are recorded as industrial residues (LER 03 01 99) therefore their accommodation is identified as potentially impacting environmentally. Association of the District of Aveiro (L. Cabral and Gil, “Multi-sectorial Study in the Area of the Environment”, 2000), in their study revealed that the “cork dust” may be responsible for geomorphological changes checked in the municipality of Santa Maria da Feira as a result of its continuous pouring.
The “cork dust” has been classified according to its source step in the transformation process of cork. In example 1 are compiled some of these types of “cork dust”.
Several efforts have been made to reuse the “cork dust”. Currently it is mostly applied as fuel for burning in furnaces either in the cork industry or even in the ceramic industry. This is due to the fact that it presents a high calorific value, which is between 20.6 and 22.2 MJ/kg (ASTM D1989). Other applications involve their use as a cargo agent, for example mixed with glues, in order to increase the quality of composites, in the production of linoleum or as a source of chemicals (extractives). The high interest of the use of Cork in the most diverse forms and applications is associated with the combination of their peculiar properties. Among others, one can mention their high friction coefficient, resilience, permeability to liquids, low thermal conductivity, low density, high absorption energy, excellent insulating and hypoallergenic properties (L. Gil, Biomass & Bioenergy 13 (1-2), p. 59, 1997; E. M. Fernandes, V. M. Correlo, J. a. M. Chagas, J. F. Mano, R.: Reis, Composites Science and Technology 70 (16), p. 2310, 2010).
These properties are not only associated with their structure but also to chemical composition. Its structure was one of the first that Robert Hooke (1635-1703) observed using an optical microscope. He has identified it as presenting an alveolar structure similar to a monolith, defined by cellular walls that form closed polyhedral cells (M. A. Fortes, M. E. Rosa, H. Pereira, A Cortica, IST Press, 2004).
The Cork's chemical composition is on average constituted by: 45% suberin, 27% lignin, 12% polysaccharides, 6% waxy substances, and 6% tannins (APCOR, Portuguese Cork Association).
It is also worth mentioning that often the Cork as a natural material is included in the group of lignocellulosic materials, despite being chemically and structurally distinct, leading imperatively to results and/or different technological alternatives for their reuse. In order to clarify and expose the alternative followed and described in this patent, additional comparisons with alternatives used in lignocellulosic materials are included.
With regard to the search for innovative alternatives for the reuse of residues of natural sources, there has been in recent decades a particular interest in exploring via chemical extraction and/or reactional conversion of potential compounds included in the chemical composition of these renewable natural sources.
From all the lignocellulosic materials, the wood is the one most similar to the cork in terms of chemical composition. It is also one of the most studied in terms of its liquefaction and subsequent application in various formulations (Pan H., Renewable and Sustainable Energy Reviews 15 (7) p. 3454, 2011).
The cork in particular has revealed some potential as a source of polyols for formulations (S. P. Silva, M. A. Sabino, E. M. Fernandes, V. M. Correlo, Boesel, R. L, Reis, International Materials Reviews 50 (6) 345, 2005).
On the other hand, focus was given from early times to the reuse of “cork dust” due to its power of auto-adhesivety. Luis M. C. C. Gil (PT Patent n° 88239, Agosto de 1988) proposed their reuse through the adhesive properties and/or peculiar binders of some of its components. In this invention, the author has developed a process for producing agglomerated cork dust, through a pre-depolymerization suberin and subsequent polymerization by pressing and heating. In this final step of the polymerization process of chemical constituents of agglutination is promoted (waxes and the suberin monomers), by allowing the agglutination of cork dust.
Several methods have been proposed and/or developed in order to obtain a liquid phase of polyols from a solid material. These are mostly suitable for various types of natural-based materials, such as lignocellulosic. However, these methods present procedural limitations, or are associated with some complexity or do not allow the maximization of liquefied materials into value added products such as “cork dust”.
A good example of a method for obtaining a polyols liquid is referred to be the process used in the patented work by G. Alexandro, C. C. Pinto, J. Joaquim, P. Neto and Carlos, patent application WO 2010/020903, Fevereiro, 2010. These inventors developed a liquefaction method of various natural materials, mostly from forestall origin, agricultural residues or from the food industry source, for the production of a liquid polyols. The authors also include in particular materials such as the “cork dust” and wood. Their method consists in resorting to oxypropilation as a reaction process of liquefaction, which is based on two essential steps: a) pre-treatment or pre-functionalization of the substrate (natural material) with an alkaline alcoholic solution for about 30 to 90 minutes, which will promote a high conversion obtaining a residual substrate of 3% residual after liquefaction; b) liquefaction of the substrate through the reaction of the previous mixture with propylene oxide (oxypropilation) in a range of temperatures between 150-200° C. and under pressure. In the particular case of “cork dust”, maximum pressures of 10-20 bar were used.
Although this method suggests similar steps to the method proposed on this patent, this is however significantly distinct. The process for obtaining polyols claimed in this patent was adapted from the method proposed by M. Kunaver, N. Cuk, E. Ukaityte, F. Kovacs, S. Opresnik and T. Katrasnik (WO/2012150043). The method here proposed allows the attainment of a high conversion upon liquefaction, avoiding the need to perform the reaction process under pressure. This novel procedure also allows the operation to be conducted at a lower range of temperatures (150-170° C.), as well as a significant reduction of reaction time (15 min) with higher conversions (95 percent). These points allow a significant optimization not only in terms of the procedure cost, but as well as in terms of energetics. The process claimed in this patent is distinguished by obtaining a polyol liquid through extraction using an extracting agent, such as water. That in turn allows one to obtain two value-added products: a mixture of polyols of higher purity which can be used not only in the suggested applications, in the patent application WO/2010/020903, but also in other applications/products that require a higher purity of its components. They can also be applied in the development of new ecological glues that use this source of polyols. This novel procedure also allows the separation of an organic phase, or liquefied cellulosic materials similar to the one obtained by liquefaction of wood, which presents an attractive fuel power with possible applications in in combustion systems such as engines.
Other methods that allow one to obtain the composition of polyols through natural materials have been proposed, but none of them proved to be suitable for “cork dust”. Between these is the method proposed in the patent application WO 2004/011518, February 2004. Succinctly, this patent describes a method for producing a composite of polyols by liquefaction of waste obtained from crops (rice, oats, corn, wheat, apple pulp, sunflowers, beet pulp). This method beyond the kind of natural substrate it differs from the one here mentioned essentially in terms of the reactional conditions, among them: the catalyst type and reaction time. The potential of the method here proposed lies mainly in the shortest reaction time for similar conversions. It is also suitable for processing “cork dust”, and in turn, taking as an example of their application as a gluing component of lignocellulosic materials, curing times and temperatures obtained are lower than those suggested in the patent application WO 2004/011518.
In relation to suggested applications for this type of liquefied materials, are generally found as components of polymer formulations. Nonetheless with limited reference to any adhesive capacity, with some exceptions, such as, the previously mentioned patent application, patent application WO 2004/011518. Such adhesive properties are however easily found when using synthetic components, such as those proposed in U.S. Pat. No. 5,932,680, August 1999. Briefly, this patent describes the possibility of the use of poly-isocyanates and polybutanodiol in the formulation of polymers and pre-polymers with properties that enable their use as adhesives after application of heat.
There are other documents that refer to the use of reagents or in the same chemical family that present in the composition of elastomers, adhesives, adhesives and ligands, one should mention in particular the US documents US 2001/3509, US 2003/0212227, US 2004/122176, US 2005/0010013 that offer formulations for polymers and pre-polymers which can be used as surfaces stickers, slabs, glass, ceramics, lignocellulosic materials, among others. Additionally, these adhesive abilities referred in these patented works are not suitable for the preparation of particle clusters. There are however some other methods that offer synthetic formulations for the gluing of lignocellulosic materials particles in the form of clusters has been proposed by C. Phanopoulos, R. H. Carr, G. Pans, patent application US 2011/0210466, September 2011.
Additionally, natural components, in particular from cork derivatives have been coupled to these synthetic origin adhesives and/or other polymer-based matrices (E. M. Fernandes, V. M. Correlo, J. a. M. Chagas, J. F. Mano, R.: Reis, Composites Science and Technology 70 (16), p. 2310, 2010), in order to facilitate the improvements in the properties of the resulting composites. The positive effect of the inclusion of cork particles in polymeric matrices, in particular with adhesive properties (glues), is associated to their peculiar properties. On one hand, cork is a material that provides thermic and sound insolation, and additionally it is also an excellent vibration absorber as a result of its closed cell structure containing air. This structure confers to it the ability to deform when subject to stress forces, such as impact or compression, acting as a buffer mode, i.e. an energy absorber, associated to the stress forces. As a general rule, the synthetic glues with good adhesive properties and when cured, are brittle and as such are associated with a deterioration of their resiliency properties when subjected to such stress forces, promoting the appearance of fissures. By this reason materials such as cork particles have been included in adhesive formulations, as proposed by V. Bonacini (Patent EP 1 347 107, November 2001). On the other hand, and as mentioned on this patent, cork particles promote equally the cohesion of the components that make up the polymer matrix, not only by filling existing porosity, but essentially by the increase of surface area that promotes a more effective mechanical connection of the various components of the array, and may also act as load for the thickening of the formulation. Additionally, his power of auto-adhesively (waxes, and suberin monomers as hinders) also offers the ability to act as a binding agent of compatible components by a chemical bond. One should note that this ability depends on the particle size and the interfacial adhesion between the matrix and the cork. Commonly, this capability is promoted by the glues heating (hot-melt adhesives).